The invention concerns a device for heat treatment of bodily tissue.
Heat treatment yields good treatment results with certain types of disease conditions involving unnatural growth of tissue. The tissue is heated to the extent that it dies. Examples of such disease conditions are certain types of cancer and benign prostate hyperplasia, BPH. During treatment certain portions of the tissue are heated so that tissue death ensues, while other portions of tissue must or should be protected. The temperature in the area of treatment should be at least 50xc2x0 C. Duration of treatment is typically 1 hour but can be shorter. The disease conditions that are primarily indicated are those which occur in tissue surrounding cavities in the body, for example the prostatic gland.
Different devices can be used in order to induce heating. Devices for heating by means of laser as well as with microwaves and radio frequencies are common. A technique is known through U.S. Pat. No. 5,257,977, according to which a catheter is provided with a reservoir for fluid. The reservoir is flexible and is connected via channels through the catheter with a heating device located outside the body. A fluid is heated in a heating device and circulated through the channels and the reservoir. The rise of temperature in the reservoir brings about heating of the surrounding tissue.
Since the channels pass through tissue that should not be treated, they must be heat insulated. According to U.S. Pat. No. 5,257,977 the heat insulation is brought about by means of a space filled with gas that surrounds the channels. The function of the heat insulation is very important, for which reason great care and considerable expense must be devoted to this part of the treatment catheter.
A more highly developed catheter for treatment is shown and described in WO 97/02794, according to which a heating device is contained inside an expandable reservoir. The heating device is provided with energy from an assembly outside of the body for heating of fluid inside the reservoir. Some of the disadvantages involving undesirable heating of certain tissue are avoided in this manner. The heating device is designed according to WO 97/02794 as a resistance wire or similar and heats the fluid through convection. The heat transferred from the fluid to the surrounding tissue gives locally good results. A disadvantage is that the effect in the tissue at a farther distance from the reservoir is insignificant.
Heat-treating with a treatment catheter that is equipped with a microwave antenna is also known with the mentioned course of disease. Examples of such microwave treatment are known previously through U.S. Pat. Nos. 5,480,417 and 5,234,004. Characteristic for previously known microwave treatment is that the prostate tissue is heated with microwaves. The intention is to heat parts of the prostate gland so that the tissue coagulates, i.e. dies. The element that emits the microwave radiation consists of a coaxial cable With an antenna at its end that is included in a catheter for treatment. Cooling fluid circulates through the catheter. The intention with the cooling is to protect the prostatic urethra, that is to say the part of the urethra that runs through the prostate gland from being affected and damaged by the heat that is generated by the microwaves. Another reason for cooling the catheter is to transport away waste heat in the coaxial cable.
It has long been viewed as important to protect the part of urethra that passes through the prostatexe2x80x94the prostatic urethraxe2x80x94during microwave treatment of benign prostate enlargement. This protection of the prostatic urethra hinders the treatment from being really effective, however, since parts of the obstructing tissue closest to the urethra are not heated but remain unaffected because of the cooling. The clinical result of heat treatment is dependent on the amount of tissue that coagulates. The degree of coagulation depends in turn on temperature in combination with the length of treatment. The temperature in turn depends on the input of energy and the carrying away of heat by the blood flow. If cooling of the prostatic urethra is done for the purpose of protecting it from being destroyed, the loss of heat energy from the area of treatment is increased, which is counterproductive and severely diminishes the effectiveness of the treatment.
There are also designs with completely uncooled treatment catheters (U.S. Pat. No. 4,967,765). In such embodiments the microwave energy must, however, be limited so that the urethra and penis are not heated due to cable losses in the coaxial cable that conducts the microwaves to the antenna. Because of this restriction, completely uncooled catheters are not preferred, since the microwave power that can then be used (max 30 Watt) is so low that one cannot achieve the high tissue temperature that is needed in order for the coagulation of tissue to occur to the desired extent.
A purpose of the invention is to increase the effectiveness of treatment with a treatment catheter of previously known technology. The higher treatment effectiveness means shorter treatment times. Alternatively, less microwave power can be used, which increases safety for the patient.
The effectiveness of treatment is increased in that a treatment catheter designed for microwave treatment of the prostate contains a fluid reservoir filled with non-circulating fluid that surrounds the microwave antenna between the prostatic apex and the bladder neck and thus prevents the prostatic urethra from being cooled during treatment The fluid reservoir is heated partly by losses in the antenna device itself that are converted to Joule heat and partly by direct absorption of microwave energy in the fluid itself. The absence of cooling of the prostatic urethra means that less microwave energy can be used to achieve the desired intra-prostatic temperature or alternatively that the treatment time can be shortened. Both possibilities are advantageous for the patient in that they increase safety for the patient and diminish the risk of damage caused by the treatment as a result of high total power output.
Further advantages and special features of the invention emerge from the following description, drawings, and dependent patent claims.